Gratuitous attacks on peaceful citizens are detestable. It would be deeply irresponsible, however, not to mention morally and intellectually obtuse, to treat all faiths and ideologies as the same. Islam entails a set of beliefs, not a set of immutable features. The widespread violence, misogyny, child abuse, tyranny, and bigotry that exists in swaths of Islamic society around the world is a product of that culture. So, if Muslims don’t believe embracing foundational American norms is a condition of good citizenry, then we have a duty to limit new immigrants from that world, because they will create divisions that other...